Melting fuses have been known for a long time. They constitute an overcurrent protective device that interrupts the electric circuit by melting a fusible conductor. The fusible conductor is heated by the current that passes through it, and it melts if the current passing through it is markedly exceeded during a certain time span.
Melting fuses heat up under a strong electric load. The resultant thermo-mechanical expansions can ultimately lead to fatigue failure of the fusible conductor.
When it comes to protecting high-voltage electric circuits in motor vehicles having an electric or hybrid drive, very high requirements are made of melting fuses that are installed in high-voltage electric circuits. An uncontrolled short circuit can destroy the entire electrical system. Moreover, there is a high risk of injury to persons located in the immediate vicinity of the high-voltage electric circuit.
For purposes of ensuring reliable functioning of the melting fuse, it is necessary to ensure that the physical and chemical properties of the melting fuse remain unchanged even after being repeatedly stressed. Consequently, it must be prevented that a fuse loses its properties due to thermo-mechanical expansions of the fusible conductor since otherwise, faulty triggering or premature failure of the fusible conductor can occur due to material fatigue.
Many development avenues are being pursued with an eye towards preventing fatigue failure of the fusible conductors in melting fuses. For this purpose, fusible conductors are affixed, for example, in solidified quartz sand or cement, a measure intended to limit their movement in case of thermal-mechanical expansion. In this context, the fusible conductor is clamped in such a way that stresses can be optimally transferred into the fixation material. For one thing, the fusible conductors are designed so as to be angled, an approach that entails the drawback of mechanical peak stresses in the individual angles of the fusible conductor, which can ultimately lead to premature fatigue failure. Other fusible conductors are affixed in the cement in a wavy or spiral shape. As a result, the spiral wire, which serves as the fusible conductor, is free of potential kinked places but it then has the same diameter over its entire length, something which, in turn, makes a fast and reliable triggering more difficult since a so-called pseudo-fuse is not present. Another disadvantage of fusible conductors affixed in cement or solidified quartz sand is the high requirements made of the production process of such a melting fuse which, in turn, translates into higher production costs.
This objective is achieved by means of a melting fuse having the features described herein.